ABSTRACT
In order to improve existing methods for the computation of design levels of the dikes along the Rhine branches in the Netherlands the hydraulic roughness of the movable minor (alluvial) bed under unsteady floodwater conditions must be predicted. For this purpose soundings of longitudinal bed profiles along pre-programmed courses have been carried out. With the help of these measurements changes in the bedformpatterns during the rise and fall of a flood have been studied. Some preliminary results are presented about the hydraulic roughness as derived from dune dimensions and grainsize and about the changes to bedform dimensions and hydraulic roughness of the alluvial bed under unsteady flow conditions.
